Autosport Labs

I am in starting to convert from MJLJ to MegaSquirt-II. Currently I have the MJLJ setup with a TPS (old board style without extra TPS circuit) which has been mapped on the rolling road and works fine. However, the MS will be mapped using a MAP sensor and I therefore need my ignition map in terms of MAP and not TPS.

So I decided what would be best to get me started with a reasonable yet safe map would be to log what the map was doing when running on the MJLJ using the MS2. I have a take off from one inlet tract (running a pair of Dellorto DHLAs) I fitted a vacuum hose to it to go to the MS2. I also spliced into the TPS signal wire and the PIP wire and took them to the MS2. I can plug my laptop into the MS2 and it tells me whats going on - great I thought I can go for a drive and record this and work out a new ignition map to start from. However, it seems to stop the MJ working. If I start the car with the MS disconnected I can see what is happening on the laptop, when I plug the MS in then the runtime display for the MJ stops working but the engine still runs. If i disconnect the MS then it all start up again. The MS shows believable values if i have the laptop connected to it. The only thing I haven't tried is using a timing light to see if the timing changes with revs or if it is in the EDIS limp home mode.

I suspect it is because I am trying to share the PIP signal - has anyone any ideas on how I can do this?

Of course it may not make much difference to the MAP vs TPS vs RPM relationship if it is running in limp home and I can still get a reasonable starting ignition map.

Thanks,
Chris

If you're suspecting the problem is around sharing the PIP signal, you may want to try feeding the tach signal to the Megasquirt by using the 'tach out' connector on the MJLJ.

...The only thing I haven't tried is using a timing light to see if the timing changes with revs or if it is in the EDIS limp home mode....

You should be able to tell just by revving the engine with and without the MS connected - limp home mode seriously affects the engines ability to change speed quickly
...or if you can drive it down the road, you will be able to tell even easier - fixed 10BTDC is a real 'limp home'!

I don't know exactly how the MS works in terms off the pressure sensor but here's another approach that should work if your confident with your electronic skills:
- power up the MS but don't connect it to PIP or the TPS (so the MJLJ/engine should run fine)
- at each rpm
-- measure the voltage at pin 1 (Vout) of the MPX4250AP in the MS
-- use the pressure vs output voltage graph in the MPX4250AP data sheet to determine the MAP
-- use the configurator run time display on the MJLJ to see what the MJLJ is reading on the TPS
...and then do some magic to equivalence the TPS and MAP.

I've not done a deliberate comparison of how the car drives with and without the MS connected. But the thing is even at 10degrees with 180bhp (when ign working) and in a 600kg car it still goes quite well!

I think the best way is probably to use the clean tacho out from the EDIS into the MS. I just need to get the settings right. Or there is the OE 60-2 crank pickup I could use - not sure if I should bother as I've put a new map together based on whatever it was doing and I'm not sure if the change in advance will make much difference to the MAP I'll see.

Well I went into work and borrowed a scope. Both the PIP and CTO are square waves at approx battery voltage. Although the pulse width of the CTO is a lot shorter than the PIP. So I moved the pickup to the CTO and the MS worked fine, also leaving the MJLJ working.

Unfortunately either my serial cable or the serial port on the laptop is dodgy because it keeps stopping and restarting communications while I am going along - its also dodgy when plugged into MJLJ.

Chris